It is an object of the present invention to provide an integrated circuit which comprises a detection arrangement for detecting the condition of saturation of at least one output transistor having a collector-emitter path through which an output current is passed. The arrangement includes a threshold circuit arranged to switch when a representative parameter of a saturation condition exceeds a given threshold.
The saturation of a transistor is manifested by a diminishing collector-emitter voltage V.sub.ce and it is a known technique to detect saturation by means of a threshold circuit which switches when the voltage V.sub.ce drops below a given threshold. Such a detection technique may thus be used to control an automatic gain control stage in order to reduce the gain of an amplifier which includes an output transistor subject to a saturation condition.
A field of application of a gain control system of this type which operates as a function of the condition of saturation of an output transistor in an amplifier, is a loudspeaker telephone set. In such a case the given threshold is to be selected in a manner such that in the worst case (small external load, high temperature), and when taking the manufacturing tolerances of the integrated circuit into account, the output transistor will never saturate. However, the result of such a choice is that one unduly restricts the maximum signal that can be obtained under normal operating conditions.